Update checkout action to latest version (#5021)
Latest checkout uses latest (non-deprecated) version of node (16 -> 20).
More information
[here](https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/):
```
Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.
```
Checkout action: https://github.com/actions/checkout
Node 20 requires a minimum of Ubuntu 20.04, so workflows currently using
18.04 are failing/will fail.
